Various welding techniques are widely used in the construction of automobile body assemblies. For example, plasma arc welding is increasingly useful in a wide variety of metal fusion bonding applications. Plasma arc welding typically involves assembling two or more metal components together to establish a weld joint location, then concentrating heat generated by an electric arc to join the metal components at the weld joint location by fusion of the parent materials of the metal components and/or by fusion of the parent materials and a filler metal, usually provided by a consumable electrode.
For example, tungsten-inert gas (TIG) welding is a process that uses arc plasma from a nonconsumable tungsten electrode that is mounted in a special welding torch and that radiates heat onto a work surface to create a weld puddle. The heat travels by conduction from the weld puddle to melt the desired depth of weld. Metal-inert gas (MIG) welding is similar to TIG welding, except that a consumable electrode is typically used and carbon dioxide may also be used for the shielding gas.
To achieve optimal weld quality, a weld bead must be shielded with a protective atmosphere to protect it against detrimental effects of oxidation prior to, during, or subsequent to joining the metal components. Accordingly, a continuous flow of gaseous flux is typically applied to the joining location to expel the ambient atmosphere to prevent oxidation and thereby promote better union of the metal components. Such gaseous flux typically involves a shielding gas composed of a chemically inert gas such as helium, argon, and the like. During welding, the gaseous flux may protect the work from oxidation, and may clean or catalytically enter into the reaction between the materials being united. Therefore, the welding torch, or a separate gas nozzle, typically blasts the top surface of the weld bead with a continuous stream of shielding gas.
Likewise, it is desirable to provide a supply of shielding gas to an underside of the weld bead, opposite of the welding torch location. Accordingly, various types of devices have been developed for supplying the underside of the weld bead with gaseous flux. But, such devices usually involve supplying a large quantity of shielding gas, which tends to be an expensive substance.
Tubular structures are often joined using TIG and MIG welding, such as in automotive body assembly operations. It is conventional in TIG and MIG welding to purge and replace the interior atmosphere of tubular structures to be welded with an inert gas. A common practice involves filling the entire tubular structure with a shield gas throughout the entire welding operation. Unfortunately, this practice tends to be wasteful and expensive because an excessive amount of shield gas gets applied to the underside of the weld bead. Alternatively, other practices involve the use of purge blocks, dams, or plugs, which provide shield gas in a more localized fashion proximate the weld bead in order to conserve shield gas. Unfortunately, however, such devices still result in the application of an unnecessary amount of shield gas. Still other practices employ rigid apparatuses for insertion within tubular structures for delivering shield gas in a more localized fashion. Unfortunately, however, such apparatuses are too inflexible to navigate bends in tubular structures and are only adapted to supply shield gas to a flat circular-shaped weld bead.
Thus, it is an object of the present invention to provide a method and an apparatus for metal fusion bonding that overcomes the shortcomings identified in the prior art above. It is a further object of the present invention to provide a method and an apparatus for metal fusion bonding wherein gaseous flux may be point-specifically applied to a relatively difficult-to-access side of a workpiece such as an underside of a weld bead within a tubular structure. It is yet a further object to provide a method and apparatus for metal fusion bonding that operates in a fixed or dynamic articulating mode and according to linear or non-linear paths.